Hierarchical-Structured Pd Nanoclusters Catalysts -PdNCs/CoAl(O)/rGO- by the Captopril-Capped Pd Cluster Precursor Method for the Highly Efficient 4-Nitrophenol Reduction.

Water-soluble captopril-capped atomically precise Pd nanoclusters (PdCapt NCs: 1.3 ± 0.5 nm) produced by a simple chemical reduction were supported on preprepared hybrid CoAl-layered double hydroxide/reduced graphene oxide (CoAl-LDH/rGO) by a pH-adjusted electrostatic adsorption strategy followed by proper calcinations, giving a series of novel catalysts -PdNCs/CoAl(O)/rGO- ( (Pd loading) = 0.09, 0.17, 0.43 wt % (ICP), = 230, 250, 280, 300, 320 °C). The characterization results show that the as-obtained catalysts possess the hierarchical nanosheet array morphology. Pd NCs with a size of ∼1.3 to 1.8 nm are highly distributed at the edge sites of the CoAl(O) nanosheets. All of the -PdNCs/CoAl(O)/rGO- catalysts show superior catalytic efficiency for the conversion of 4-nitrophenol to 4-aminophenol, particularly 0.17-PdNCs/CoAl(O)/rGO-300 possesses the highest performance with a turnover frequency (TOF) of 30 042 h, which is the highest among the reported Pd-based catalysts so far. The superior activity of 0.17-PdNCs/CoAl(O)/rGO-300 can be owing to ultrafine Pd NCs with a clean surface, the strongest PdNCs-Co-OH(LDH)-rGO three-phase synergy, and the much improved adsorption of the substrate via π-π stacking upon nanosheet array morphology. Meanwhile, 0.17-PdNCs/CoAl(O)/rGO-300 exhibits excellent catalytic activities for various nitroarenes and anionic azo dyes as well as good reusability with the complete reduction of 4-nitrophenol (4-NP) within 90 s after 10 successive runs. The present work provides not only a simple and convenient strategy for the synthesis of clean, efficient, and environmentally friendly supported metal nanocluster catalysts but also a new idea for the efficient catalytic degradation of environmental pollutants.